Method and apparatus for providing virtual ports with attached virtual devices in a storage area network

ABSTRACT

Systems particularly a virtualization switch or a storage device, which include virtual ports connected to virtual devices with virtual worldwide names and virtual LUNs. Because Fibre Channel environment hosts can track worldwide names from one port to another and allow continuity in that regard, the virtual worldwide names are provided with relevant virtual LUNs and connected these to virtual ports so that the virtual devices can be moved as desired to overcome failures or to allow load balancing.

CROSS REFERENCE TO RELATED APPLICATIONS

This continuation application claims priority to U.S. patent applicationSer. No. 10/356,659, entitled “Method and Apparatus for ProvidingVirtual Ports with Attached Virtual Devices in a Storage Area Network,”filed Jan. 31, 2003, which is hereby incorporated by reference.

This application is also related to and incorporates by reference, U.S.patent application Ser. Nos. 10/209,743, entitled “Method And ApparatusFor Virtualizing Storage Devices Inside A Storage Area Network Fabric”by Naveen S. Maveli, Richard A. Walter, Cirillo Lino Costantino,Subhojit Roy, Carlos Alonso, Michael Yiu-Wing Pong, Shahe H. Krakirian,Subbarao Arumilli, Vincent Isip, Daniel Ji Yong Park Chung, Stephen D.Elstad and Dennis Makisihma, filed Jul. 31, 2002; 10/209,742, entitled“Host Bus Adaptor-Based Virtualization Switch” by Subhojit Roy, RichardA. Walter, Cirillo Lino Costantino, Naveen S. Maveli, Carlos Alonso, andMichael Yiu-Wing Pong, filed Jul. 31, 2002; 10/209,694, entitled“Hardware-Based Translating Virtualization Switch” by Shahe H.Krakirian, Richard A. Walter, Subbarao Arumilli, Cirillo LinoCostantino, L. Vincent M. Isip, Subhojit Roy, Naveen S. Maveli, DanielJi Yong Park Chung, Stephen D. Elstad, Dennis H. Makishima, and DanielY. Chung, filed Jul. 31, 2002 such applications hereby beingincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to storage area networks, and moreparticularly to virtualization of ports, devices and logic units of suchstorage area network.

2. Description of the Related Art

As computer network operations have expanded over the years, storagerequirements have become very high. It is desirable to have a largenumber of users access common storage elements to minimize the cost ofobtaining sufficient storage elements to hold the required data.However, this has been difficult to do because of the configuration ofthe particular storage devices. Originally storage devices were directlyconnected to the relevant host computer. Thus, it was required toprovide enough storage connected to each host as would be needed by theparticular applications running on that host. This would often result ina requirement of buying significantly more storage than immediatelyrequired based on potential growth plans for the particular host.However, if those plans did not go forward, significant amounts ofstorage connected to that particular host would go unused, thereforewasting the money utilized to purchase such attached storage.Additionally, it was very expensive, difficult and time consuming totransfer unused data storage to a computer in need of additionalstorage, so the money remained effectively wasted.

In an attempt to solve this problem storage area networks (SANs) weredeveloped. In a SAN the storage devices are not locally attached to theparticular hosts but are connected to a host or series of hosts througha switched fabric, where each particular host can access each particularstorage device. In this manner multiple hosts could share particularstorage devices so that storage space could be more readily allocatedbetween the particular applications on the hosts. While this was a greatimprovement over locally attached storage, the problem does develop inthat a particular storage unit can be underutilized or fills up due tomisallocations or because of limitations of the particular storageunits. So the problem was reduced, but not eliminated.

To further address this problem and allow administrators to freely addand substitute storage as desired for the particular networkenvironment, there has been a great push to virtualizing the storagesubsystem, even on a SAN. In a virtualized environment the hosts willjust see very virtual large disks of the appropriate size needed, thesize generally being very flexible according to the particular hostneeds. A virtualization management device allocates the particular needsof each host among a series of storage units attached to the SAN.Elements somewhere in the network would convert the virtual requestsinto physical requests to the proper storage unit.

Another problem that has occurred in SANs is the inability to movelogical unit numbers (LUNs) around inside a storage unit. Whilevirtualization may help hide particular volumes and the physicallinkages from the hosts, the virtualization system still will directactivity to a particular port and LUN. However, if there are particularproblems, as in a failure of a particular unit, it would be desirable tomove the particular LUN to a different location. Alternatively, it wouldbe desirable to be able to move LUNs and ports to load balance thesystem to allow better overall throughput. However, existing units donot allow this flexibility because a particular LUN is tied to aparticular physical port and therefore cannot be readily moved. Thusthere currently are problems if a physical unit fails or if the systemis not properly load balanced.

BRIEF SUMMARY OF THE INVENTION

Systems according to the present invention, particularly avirtualization switch or a storage device, include virtual portsconnected to virtual devices with virtual worldwide names and virtualLUNs. Because Fibre Channel environment hosts can track worldwide namesfrom one port to another and allow continuity in that regard, it isdesirable to provide virtual worldwide names with relevant virtual LUNsand connect these to virtual ports so that the virtual devices can bemoved as desired to overcome failures or to allow load balancing.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a general view of a storage area network (SAN);

FIG. 2 is a block diagram of a SAN showing the location of avirtualization switch;

FIG. 3 is a block diagram of a SAN showing virtual ports, devices andlogical units according to the present invention;

FIG. 4 is a block diagram of a first embodiment of a virtualizationswitch according to the present invention;

FIG. 5 is a block diagram of a second embodiment of a virtualizationswitch according to the present invention;

FIGS. 6A, 6B, and 6C are illustrations of a virtualization switch with aseries of virtual ports and virtual LUNs in an original configurationand two alternative configurations.

FIG. 7 is a flowchart of operations to first register and then move thevirtual ports, devices and LUNs between different physical ports.

FIG. 8 is a block diagram of an exemplary storage unit.

FIG. 9 is a logical diagram of the storage unit of FIG. 8.

FIGS. 10A, 10B, and 10C are the original connections of a storage unitaccording to the present invention followed by a port failure in thatunit and a reconfiguration of that unit to address the failure.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a storage area network (SAN) 100 generallyillustrating a prior art design is shown. A fabric 102 is the heart ofthe SAN 100. The fabric 102 is formed of a series of switches 110, 112,114, and 116, preferably Fibre Channel switches according to the FibreChannel specifications. The switches 110-116 are interconnected toprovide a full mesh, allowing any nodes to connect to any other nodes.Various nodes and devices can be connected to the fabric 102. Forexample a private loop 122 according to the Fibre Channel loop protocolis connected to switch 110, with hosts 124 and 126 connected to theprivate loop 122. That way the hosts 124 and 126 can communicate throughthe switch 110 to other devices. Storage unit 132, preferably a unitcontaining disks, and a tape drive 134 are connected to switch 116. Auser interface 142, such as a workstation, is connected to switch 112,as is an additional host 152. A public loop 162 is connected to switch116 with disk storage units 166 and 168, preferably RAID storage arrays,to provide storage capacity. A storage device 170 is shown as beingconnected to switch 114, with the storage device 170 having a logicalunit 172 and a logical unit 174. It is understood that this is a verysimplified view of a SAN 100 with representative storage devices andhosts connected to the fabric 102. It is understood that quite oftensignificantly more devices and switches are used to develop the full SAN100.

Referring now to FIG. 2, a block diagram according to the preferredembodiment of the invention is illustrated. In FIG. 2 the hosts 200 areconnected to a SAN fabric 250. Similarly, storage arrays 204 are alsoconnected to the SAN fabric 250. However, as opposed to the SAN fabric102 that is made with conventional Fibre Channel switches, the fabric250 includes a virtualization switch 252, which acts as a virtualizationagent 254. A management server 218 is connected to the fabric 250 tomanage and provide information to the virtualization switch 252 and tothe hosts 200. As the virtualization switch 252 can provide thevirtualization remapping functions at wire speed, performance is not aparticular problem and this solution can much more readily handle muchlarger fabrics by the simple addition of additional virtualizationswitches 252 as needed. For more details on virtualization and avirtualization switch, please refer to the applications incorporatedabove.

FIG. 3 illustrates the embodiment of FIG. 2 except that thevirtualization switch 252 has been changed to a virtualization switch352 with a series of virtual ports 300, 302, and 304. These virtualports are logically connected, respectively, to virtual worldwide named(WWN) devices 306, 308, and 310. Each of these virtual WWN devicesincludes two virtual logic units or LUNs 312-322. In operation, thehosts 200 would address a particular virtual port, for example, virtualport 1 300 which would be the port connected for the virtual worldwidenamed device 306, which would include virtual LUNs A and B, 312 and 314.The virtual LUNs A and B 312 and 314 are the virtualized LUNs providedby the management server 218 to the hosts 200, with packets to thoseLUNs converted by the virtualization switch 352 into the proper physicalpackets. Thus the virtual LUNs and virtual worldwide named devices wouldmap to various locations in the storage arrays 204 based onconfiguration information provided by the management server 218.However, the particular hosts 200 would believe that they were ports,devices and LUNs connected to the virtualization switch 352. Asdescribed below, because they are virtual ports, virtual worldwidenames, and virtual LUNs, they can be readily moved by the virtualizationswitch 352 and connections from the particular hosts to the particularvirtual LUNs can be changed to improve load balance or to provide forequipment failures.

FIG. 4 illustrates a virtualization switch 400 according to the presentinvention. A plurality of HBAs 402 are provided to connect to the fabricof the SAN. Each of the HBAs 402 is connected to an ASIC referred to theFeather chip 404. The Feather chip 404 is preferably a PCI-X to PCI-Xbridge and a DRAM memory controller. Connected to each Feather Chip 404is a bank of memory or RAM 406. This allows the HBA 402 to provide anyframes that must be forwarded for further processing to the RAM 406 byperforming a DMA operation to the Feather chip 404, and into the RAM406. Because the Feather chip 404 is a bridge, this DMA operation isperformed without utilizing any bandwidth on the second PCI bus. Each ofthe Feather chips 404 is connected by a bus 408, preferably a PCI-X bus,to a north bridge 410. Switch memory 412 is connected to the northbridge 410, as are one or two processors or CPUs 414. The CPUs 414 usethe memory 412 for code storage and for data storage for CPU purposes.Additionally, the CPUs 414 can access the RAM 406 connected to each ofthe Feather chips 404 to perform frame retrieval and manipulation asillustrated in FIG. 12. The north bridge 410 is additionally connectedto a south bridge 416 by a second PCI bus 418. CompactFlash slots 420,preferably containing CompactFlash memory which contains the operatingsystem of the switch 400, are connected to the south bridge 416. Aninterface chip 422 is connected to the bus 418 to provide access to aserial port 424 for configuration and debug of the switch 400 and to aROM 426 to provide boot capability for the switch 400. Additionally, anetwork interface chip 428 is connected to the bus 418. A PHY,preferably a dual PHY, 430 is connected to the network interface chip428 to provide an Ethernet interface for management of the switch 400.In normal operation, the HBA 402 receives a packet and analyzes theheader. If a table entry is present in the RAM 406 indicating the packetis directed to a virtual device, the proper information, either physicalstorage unit or host, is retrieved and the header fields changed toredirect the packet. The altered packet is then provided from the HBA402. For more details of operation, please refer to the applicationsincorporated above.

Proceeding now to FIG. 5, a diagram of a virtualization switch 500according to the present invention is illustrated. In the virtualizationswitch 500 a pair of FPGAs 502, referred to as the pi FPGAs, provide theprimary hardware support for the virtualization translations. Four BloomASICs 504 are interconnected to form to Bloom ASIC pairs. A moredetailed description of the Bloom ASIC is provided in U.S. patentapplication Ser. No. 10/124,303, filed Apr. 17, 2002, entitled “FrameFiltering of Fibre channel Frames,” which is hereby incorporated byreference. One of the Bloom ASICs 504 in each pair is connected to oneof the pi FPGAs 502 so that each Bloom ASIC pair is connected to both piFPGAs 502. Each of the Bloom ASICs 504 is connected to a series of fourserializer/deserializer chips and SFP interface modules 506 so that eachBloom ASIC 504 provides four external ports for the virtualizationswitch 500, for a total of sixteen external ports in the illustratedembodiment. Also connected to each pi FPGA 502 is an SRAM module 508 toprovide storage for the 10 tables utilized in remapping and translationof the frames. Each of the pi FPGAs 502 is also connected to a VER orvirtualized exchange redirector 510, also referred to as avirtualization engine. The VER 510 includes a CPU 512, SDRAM 514, andboot flash ROM 516. In this manner, the VER 510 can provide high-levelsupport to the pi FPGA 502 in the same manner as the CPUs 414 in thevirtualization switch 400. A content addressable memory (CAM) 518 isconnected to each of the pi FPGAs 502. The CAM 518 contains the VER maptable containing virtual disk extent information.

A PCI bus 520 provides a central bus backbone for the virtualizationswitch 500. Each of the Bloom ASICs 504 and the VERs 510 are connectedto the PCI bus 520. A switch processor 524 is also connected to the PCIbus 520 to allow communication with the other PCI bus 520 connecteddevices and to provide overall control of the virtualization switch 500.A processor bus 526 is provided from the processor 524. Connected tothis processor bus 526 are a boot flash ROM 528, to enable the processor524 to start operation; a kernel flash ROM 530, which contains theprimary operating system in the virtualization switch 500; an FPGAmemory 532, which contains the images of the various FPGAs, such as piFPGA 502; and an FPGA 534, which is a memory controller interface tomemory 536 which is used by the processor 524. Additionally connected tothe processor 524 are an RS232 serial interface 538 and an Ethernet PHYinterface 540. Additionally connected to the PCI bus 520 is a PCI IDE orintegrated drive electronics controller 542 which is connected toCompactFlash memory 544 to provide additional bulk memory to thevirtualization switch 500. Thus, as a very high level comparison betweenswitches 400 and 500, the Bloom ASICs 504 and pi FPGAs 502 replace theHBAs 402 and the VERs 510 and processor 524 replace the CPUs 414. Innormal operation, a pi FPGA 502 receives a packet and analyzes theheader. If a table entry is present in the SRAM 508 indicating thepacket is directed to a virtual device, the proper information, eitherphysical storage unit or host, is retrieved and the header fieldschanged to redirect the packet. The altered packet is then provided fromthe pi FPGA 502 to the Bloom ASIC 504 and then to the fabric. Again, formore details of operation, please refer to the applications incorporatedabove.

Referring now to FIG. 6A, a virtualization switch 600 is shown. Avirtualization switch 600 includes four physical ports 602, 604, 606,and 608. It is also represented as including four virtual ports 610,612, 614, and 616. According to the preferred embodiment of the presentinvention, each virtual port corresponds to a virtual device with avirtual WWN. Each of the virtual ports 610-616 also includes two virtualLUNs 618-632 as illustrated. In the illustration of FIG. 6A virtual port1 610 and virtual port 2 612 are mapped to physical port 602 by thevirtualization switch 600. That is, any frames directed to virtual port1 600 or virtual port 2 612 will be provided to the virtualizationswitch 600 over the physical port 1 602. This would be done by havingvirtual ports 1 and 2 610 and 612 utilize different AL_PA addresses orlower byte of the Fibre Channel address while retaining the same highand middle bytes as the physical port 1 602. Thus, switches in thefabric would route based on the high and middle bytes, the domain andarea or port bytes, so the frames would be routed to physical port 1602. The virtualization switch 600 would then interpret these framesaccording to the full twenty-four bit address, using the lower byte todistinguish virtual ports/virtual devices. Similarly, the virtual port 3614 and virtual port 4 616 are shown as being associated with thephysical port 2 604. As can be seen, this would mean that two virtualports and four virtual LUN devices would be connected through each oftwo physical ports and two of the physical ports would have no virtualdevices whatsoever. This would thus present a relatively imbalancedsituation.

This imbalance is corrected as shown in FIG. 6B. In this case there is aone-to-one mapping so each virtual port is connected to a singlephysical port. Thus physical port 1 602 is connected to virtual port 1610, virtual port 2 604 is connected to virtual port 2 612 and so on. Inthis case, assuming relatively equal flow of traffic to the virtualports, there would be relatively equal use of resources on the variousphysical ports. This would result in a more balanced situation in theSAN.

FIG. 6C illustrates a potential failure condition where communicationusing physical port 1 602 is disrupted. This could be due to a failureof the link to physical port 1 602, failure of the virtualization switch600 (or physical port 1 602) or other reasons. In this case thevirtualization switch 600 has reconfigured so that virtual ports 1 610and virtual ports 2 612 have been connected logically to physical port 3606. This would be done by simply changing the middle byte of the FibreChannel address, as the domain or high byte would remain the samebecause it would still be the virtualization switch 600. The lower byteor AL_PA or loop address would remain the same, indicating virtual ports1 and 2 610 and 612. A flow chart of initialization and operation ofthis movement is shown in FIG. 7.

Referring then to FIG. 7, in step 700 the virtualization switch 600FLOGIs the SAN to begin its initialization. In doing this the variousphysical ports of the virtualization switch 600 would be identified tothe SAN, as would the virtualization switch itself. Next, in step 702,the virtualization switch 600 would provide a frame to the managementserver indicating which virtual ports are available and their relatedvirtual worldwide names. This relationship is desirable because FibreChannel hosts track resources based on worldwide names on a morepermanent basis, as the worldwide names are unique. Thus, the managementserver 218 needs to know which virtual ports are present to enableproper routing and to know what the related virtual worldwide names areto allow reconfiguration. In step 704 the management server 208 definesthe particular virtual LUNs in the virtualization system and ties thoseto the virtual or V-ports and virtual worldwide names (VWWNs) providedby the virtualization switch 600. In step 706 the management server 218tells the virtualization switch 600 of the total relationship betweenthe V-LUNs, V-ports, and VWWNs. This is generally also where themanagement server 218 would provide the virtual to physical mappings ofthe various VLUNs. In step 708 the virtualization switch 600 thenregisters, using FLOGI frames or other techniques, the VWNNs/V-portswith the name server of the SAN so that for all apparent purposes aseries of virtual devices referred to by the VWWNs and connected to theV-ports are connected to the virtualization switch 600.

The virtualization switch 600 preferably registers the virtual devicesas FCTYPE 8, SCSI, so that the hosts 200 can use SCSI commands, as theywould with the physical storage units. In step 710, with thisinitialization complete, a host 200 will then discover the particularVWNNs of the virtualization switch 600 and perform a PLOGI and PRLI toeach one of the particular WNNs to discover what the device is and whatits capabilities are. The virtualization switch 600 would emulate thedevices and provide appropriate responses. The host 200 will then useFibre Channel FCP SCSI frames, such as Inquiry for SCSI-2 or Report LUNsfor SCSI-3, to query each particular device to determine the particularvirtual LUNs for each device. Again, the virtualization switch 600 wouldemulate the devices and provide appropriate responses, including theVLUN information. In this manner the host 200 will be able to have acomplete FCP address for each of the virtual LUNs. In step 712 an eventwhich causes the V-LUNs to move is assumed to occur. As noted above,this could be a desire to load balance or it could be a physical failureof a particular component. In step 714, the virtualization switch 600unregisters an exemplary VWNN 1 and V-port 1 from the SAN. Then in step716, the VWWN 1, the virtual device has been just unregistered, islinked to a new physical port by the virtualization switch 600 and thusbecomes V-port l′ because of the change of the middle byte of the FibreChannel address. For example, V-port 1 would have an address of D1, P1,2, while V-port 1′ would have an address of D1, P2, 2. While it ispreferred to keep the AL_PA of the V-port the same, it can be changed ifdesired or if needed.

In step 718, the VWWN 1 and V-port l′ are registered by thevirtualization switch 600 with the name server so that once again theparticular device is present. Note that it has not been required to tellthe management server 218 of this change with the management server 218then reconfiguring each host 200, as the logic is already present incurrent Fibre Channel hosts to handle the moving of devices and LUNsbetween particular ports. But it would be advantageous to inform themanagement server 218 of the change so it can keep its tables coherentfor use with future hosts.

In step 720 the host 200, now noting that there has been a new deviceadded, rediscovers VWWN 1 at V-port 1′ using PLOGI/PRLI commands andthen using FCP commands to discover the particular V-LUNs that are stillattached to the VWWN 1. In this case the host 200 will know theparticular device has moved ports and the same LUNs are presented. Thusthe particular LUNs will have moved from one physical port to anotherwithout requiring any actual physical reconfiguration of any particulardevices. Thus, by configuration changes and softwareregistration/unregistrations it is possible to move a particular virtualdevice and its virtual LUNs from one physical port to another to allowload balancing or fault tolerance.

The preferred operation of unregistering and registering the virtualport is preferred because it provides smoother operation. However, theunregistration could be omitted, leaving that to normal Fibre Channelfailure mechanisms.

The above has been described with relation to a virtualization switch ina SAN. However, it also similarly applies to a storage unit 800. Shownin FIG. 8 is an exemplary storage unit 800. There are two host busadapters (HBAs) 802 and 804 which provide the Fibre Channel connectivityfor the storage unit 800. These are connected by a backbone bus 806 to aCPU 808, which performs management and control operations of the storageunit 800. They are also connected to a RAID engine 810 because in theexemplary embodiment the storage unit 800 is a RAID unit. The RAIDengine 810 in turn is connected in the illustrated embodiment to an HBA812 which is connected to a Fibre Channel loop 814 containing fourphysical disk drives 816, 818, 820 and 822. Also shown for illustrativepurposes the RAID engine 810 is connected to a SCSI controller 824,which has a SCSI bus 826 connected to physical disk drives 828, 830,832, and 834. This combined use of a Fibre Channel loop and a SCSI busis exemplary as it would not be normal in a typical storage unit 800.This is the physical representation of the storage unit 800 and alogical representation of the storage unit 800 to a host 200 would bethat it would be a single WWN for each HBA, with a series of LUNs, tiedto that HBA, with the RAID engine 810 properly striping the LUN dataacross the various disk drives. This is conventional.

This logical relationship is shown in more detail in FIG. 9. The storageunit 800 includes a disk unit 850 with physical ports 852 and 854.Physical port 852 is connected to a LUN 860, while physical port 854 isconnected to a LUN 862. This is the normal configuration for a storageunit.

The preferred embodiment of a storage unit 900 is shown in FIG. 10A. Adisk unit 950 has two physical ports 952 and 954. It also has twovirtual ports 956 and 958. A LUN 960 is connected to virtual port 956and a LUN 962 is connected to virtual port 958. In this originalconfiguration, physical port 952 is mapped to virtual port 956 andphysical port 954 is mapped to virtual port 958. As in thevirtualization switch example, the virtual ports are distinguished fromthe physical ports by use of the AL_PA bits. It is understood that FIG.10A is a simplification in that it only shows one fabric and that aconventional HBA includes two ports which are connected to redundantfabrics. However, the drawing is illustrative.

FIG. 10B illustrates the disk storage unit 900 except that the physicalport 952 is no longer operational for a multitude of causes, such as thelink being disabled, the physical port being disabled or other reasons.Thus, communications to LUN 960 are stopped. Referring to FIG. 10C, thestorage unit 900 then reconfigures the disk unit 950 so that virtualport 956 is now logically connected to physical port 954 so that LUN 960is still accessible by the host devices. The performance may be somewhatdiminished in this operation but the LUN 960 is still fully accessible,unlike situations in the prior art where the LUN 960 would no longer beaccessible.

While the above descriptions illustrate moving the virtual WWNs andvirtual ports between physical ports on a single physical device, withproper coordination the virtual device represented by the virtual WWNcould readily be moved between two different physical devices. In thiscase, the domain or upper byte of the address would change and themiddle byte or area or port byte may change.

As illustrated by these descriptions of the preferred embodiments,systems according to the present invention allow movement of virtualdevices and LUNs to different physical ports, thus allowing loadbalancing or improved fault tolerance.

While the invention has been disclosed with respect to a limited numberof embodiments, numerous modifications and variations will beappreciated by those skilled in the art. It is intended, therefore, thatthe following claims cover all such modifications and variations thatmay fall within the true spirit and scope of the invention.

1. (canceled)
 2. An apparatus, comprising: a plurality of network ports,a first port of said plurality of network ports to provide for apparentlinkage to a device, a first address of the device being associated withsaid first port of said plurality of network ports, so that a worldwidename of the device is associated with said first port of said pluralityof network ports; and an element that provides a second addressassociated with said worldwide name to provide for apparent linkage to adifferent port of said plurality of network ports than would be providedusing said first address.
 3. The apparatus of claim 2, wherein saidelement provides said second address when there is a communicationfailure using said first network port.
 4. The apparatus of claim 2,wherein there is additional communication traffic on at least two ofsaid plurality of network ports and wherein said element provides saidsecond address to improve communication traffic balance on the at leasttwo of said plurality of network ports.
 5. The apparatus of claim 2,wherein the device comprises a virtual device and wherein said worldwidename comprises a unique worldwide name associated with said virtualdevice.
 6. The apparatus of claim 5, wherein said virtual device furthercomprises a virtual LUN and said element responds to queries to saidvirtual device by providing said virtual LUN.
 7. The apparatus of claim2, wherein said apparatus is a storage unit and said apparatus furthercomprises at least one hard disk drive.
 8. A method implemented in anapparatus, comprising: providing, by the apparatus, for an apparentlinkage to a device by associating a first address of the device with afirst port of a plurality of ports so that a worldwide name of thedevice is associated with the first port of the plurality of networkports; and providing, by the apparatus, a second address associated withthe worldwide name to provide for an apparent linkage to a differentport of the plurality of network ports than would be provided using thefirst address.
 9. The method of claim 8, wherein said providing of thesecond address occurs when there is a communication failure using thefirst network port.
 10. The method of claim 8, wherein there isadditional communication traffic on at least two of the plurality ofnetwork ports and wherein said providing of the second address occurs toimprove communication traffic balance on the at least two of theplurality of network ports.
 11. The method of claim 8, wherein thedevice comprises a virtual device and wherein the worldwide namecomprises a unique worldwide name associated with the virtual device.12. The method of claim 11, wherein the virtual device further comprisesa virtual LUN and the method further comprises responding, by theapparatus, to queries to the virtual device by providing the virtualLUN.
 13. The method of claim 8, wherein the apparatus is avirtualization switch.
 14. The method of claim 8, wherein the apparatusis a storage unit.
 15. A fabric comprising: a first apparatus,comprising: a plurality of network ports, a first port of said pluralityof network ports to provide for apparent linkage to a device, a firstaddress of the device being associated with said first port of saidplurality of network ports, so that a worldwide name of the device isassociated with said first port of said plurality of network ports; andan element that provides a second address associated with said worldwidename to provide for apparent linkage to a different port of saidplurality of network ports than would be provided using said firstaddress, a second device having a network port coupled to said firstnetwork port; and a third device having a network port coupled to saiddifferent network port.
 16. The fabric of claim 15, wherein said elementprovides said second address when there is a communication failure usingsaid first network port.
 17. The fabric of claim 15, wherein there isadditional communication traffic on at least two of said plurality ofnetwork ports and wherein said element provides said second address toimprove communication traffic balance on the at least two of saidplurality of network ports.
 18. The fabric of claim 15, wherein thedevice comprises a virtual device and wherein said worldwide namecomprises a unique worldwide name associated with said virtual device.19. The fabric of claim 18, wherein said virtual device furthercomprises a virtual LUN and said element responds to queries to saidvirtual device by providing said virtual LUN.